The invention is based on a current-limiting switch as claimed in the precharacterizing clause of patent claim 1.
Such current-limiting switches may be used in the high-voltage or medium-voltage areas as generator switches, as coupling switches between busbar sections in switchgear assemblies, as DC switches, or in mesh-connected networks to reduce the operational losses.
The invention refers to a prior art of current-limiting switches as is described, for example, in European Application EP Application No. 98811251.2, which has not yet been published. This switch has a high-speed mechanical switching point with galvanic contacts, and two commutation paths connected in parallel with them. A first switching apparatus and an isolating switching point are arranged in series in the first commutation path, and a current limiter and a second switching apparatus are connected in series in the second commutation path. The current limiter is designed in such a way that current which is carried by it and is commutated from the first to the second commutation path when the first switching apparatus opens is limited with a time delay. During this time delay, no overvoltage can build up across the two commutation paths, and an overvoltage-resistant isolation path can at the same time be formed in the first commutation path.
The invention, as it is specified in the patent claims, is based on the object of providing a current-limiting switch of the type mentioned initially which, thanks to its special, space-saving design and the small moving mass, allows high-speed on and off switching in the high-voltage and medium-voltage areas.
The current-limiting switching according to the invention has three paths arranged in parallel with one another, two of which contain a mechanical switching point. One of these mechanical switching points is designed to carry and switch rated current, while the other carries a commuted current, briefly and in the form of a pulse, just while switching is taking place. The contact arrangements of the mechanical switching points are designed to be axially symmetrical and are arranged coaxially. Short, coaxial copper connections result in very low stray inductances, thus allowing a current to be commutated very quickly.
If the third path of the switch according to the invention also contains a mechanical switching point with a coaxially arranged contact arrangement, there is no need for any series disconnector to be connected in series with conventional current-limiting switches.
If the contact arrangements have different diameters and they are arranged located one inside the other, the extent of the switch in the axial direction is reduced. This makes it possible to reduce the dimensions of a housing in which the contact arrangements are arranged, in order to be protected, for example, against dust and other disturbing influences. In this case, it is particularly advantageous for a contact arrangement to be arranged in a pressure-resistant housing which, for example, is filled with an insulating gas at atmospheric pressure, or at a higher pressure, and this has an advantageous effect on the dielectric properties of the contact arrangement. If the housing contains two electrically conductive parts which are insulated from one another, the rated current can be carried directly via these housing parts to the connections of the rated-current switching point. There is thus no need for any complex rated-current bushings through the housing.
If the switching points contain a high-speed drive for opening and closing the contact arrangement, it is possible to implement different algorithms, corresponding to the operational requirements, for opening and/or closing the switch.